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Building and Environment 100 (2016) 215e226

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Building and Environment

journal homepage: www.elsevier .com/locate/bui ldenv

Economic and energy consumption analysis of smart building eMEGAhouse

Min-Yuan Cheng a, Kuan-Chang Chiu a, *, Li-Chuan Lien b, Yu-Wei Wu a, Jing-Jhe Lin a

a Dept. of Civil and Construction Engineering, National Taiwan Univ. of Science and Technology, Taipei 10607, Taiwan, ROCb Fujian University of Technology, College of Civil Engineering, Fujian 350108, China

a r t i c l e i n f o

Article history:Received 16 December 2015Received in revised form24 February 2016Accepted 25 February 2016Available online 3 March 2016

Keywords:: energy efficiency and carbon reductionMEGA houseEarth-tubeSolar chimneyEconomic analysis

* Corresponding author. Tel.: þ886 2 27330004; faE-mail addresses:[email protected] (M.-Y. Ch

edu.tw (K.-C. Chiu), [email protected] (L.-C. Lien),(Y.-W. Wu), [email protected] (J.-J. Lin).

http://dx.doi.org/10.1016/j.buildenv.2016.02.0230360-1323/© 2016 Elsevier Ltd. All rights reserved.

a b s t r a c t

Energy efficiency and carbon reduction of new buildings are key objectives of policies that aim todecrease electric use nationwide, particularly during the summer, when electricity usage is at its highest.A case study was developed to test the energy-conservation performance and economic feasibility of thecreative and intelligent open building “MEGA House”. MEGA House focuses on making improvements infour key areas: (a) Material, (b) Electronic, (c) Green Building, and (d) Automation. This paper focuses onapplications in the areas of Electronic and Green Building. The economic analysis in this paper of elec-tricity consumption and of the potential energy-savings is based on the use of energy conservationequipment such as earth tubes and solar chimneys, situation simulations, field measurements at fourexperimental stages, and economic calculations.

According to the results of measurement and economic analysis, the MEGA House demonstratedoptimal energy conservation performance. Using an earth tube (fan) and a solar chimney (exhaust fans)in the MEGA House lowered the indoor temperature about 1~2 �C in summer, while using an earth tube(fan) instead of an electric heater increased the indoor temperature as much as 3e4 �C. In terms ofeconomic benefits, the using the energy-conservation facilities installed in MEGA House reduced elec-tricity expenditures by NT$8537.76 and decreased CO2 emissions by around 1288.83 kg per year.

© 2016 Elsevier Ltd. All rights reserved.

1. Introduction

Because of Taiwan's location near the tropics, electricity usageincreases significantly during the summer. Based on energy sta-tistics published by the Taiwan Power Company and Bureau ofEnergy, Ministry of Economic Affairs, R.O.C., air-conditioning ac-counts for the highest proportion (41%) of the year-round electricityconsumption of households and commercial buildings [1]. There-fore, the electricity used for the air-conditionings is overvalued. A1 �C increase in indoor temperature reduces electricity consump-tion by 6%, the equivalent of over 300,000,000 kW H in savingsnationwide in one summer [2].

Buildings are major energy consumers in modern society andthus have a critical role to play in saving energy and reducinggreenhouse gas emissions. Improvements in general building

x: þ886 2 27376606.eng), [email protected]@mail.ntust.edu.tw

construction have raised popular awareness of energy consumptionin buildings and increased the willingness of the general public toseek further energy-saving solutions [3]. One of the primary waysto improve energy conservation in buildings is to incorporate thebest energy-saving designs and renewable energy systems intonew buildings. Recently, there have been significant studies toanalyze the energy consumption in buildings and to find effectivecontrol strategies for saving energy through various ways to makebetter thermal comfort in different climate conditions (such as hotand humid climate) and building types (such as home and resi-dential, etc.) [4e8]. Especially, to achieve the thermal comfort andenergy-saving conditions, comfort natural ventilation has beenrecommended as the one of the most effective cooling strategy forbuildings in hot and humid climates [9]. Besides, the “Energy-Saving” building in Paris, France produces its own energy forheating, lighting, and air-conditioning. The cooling system for thisbuilding pumps cold water from the Seine River throughout thebuilding, which eliminates the need for air-conditioning, and usesstate-of-the-art insulation to prevent heat transmission. The sys-tems used in this building reduce electricity consumption to 16 kW

M.-Y. Cheng et al. / Building and Environment 100 (2016) 215e226216

per square meter per year [10]. In Taiwan, the Architecture andBuilding Research Institute commissioned the National TaiwanUniversity of Science and Technology research team to develop theopen-building MEGA House to explore the effects of various energyefficiency and carbon reduction measures [11]. The open-building(OB) concept integrates construction life-cycle information. TheOB philosophy has been applied in an increasing number of con-struction projects based on its successful minimization of wasteand of the need for building reconstruction [12].

The creative and intelligent open-building “MEGA House” ad-dresses the four key areas of: (1) Materials, (2) Electronics, (3)Green Building, and (4) Automation, with each implemented acrossthe MEGA House life cycle. This paper focuses on the application ofElectronics (E) and Green Building (G) and combines the smartcontrol mechanism [13] to find the highest performance combi-nation of energy-saving equipment at different times and condi-tions. In this paper, “Electronics” refers to electronic facilitynetworks. This project employed RFID technology for door entrancecontrol systems, door plates, and air-conditioning sensors and in-tegrated a smart control system to increase occupant safety,decrease energy consumption, and store essential data. “GreenBuilding” refers to the use of green building design concepts. Thegreen-building facilities used in this project include: 3-in-1 solarpanels, insulation glass, a solar chimney, and an earth tube. Thesolar panel was used to provide clean energy for the building;insulation glass was installed to deflect excess sunlight away fromthe building; the solar chimney achieved fresh air circulation atlower power consumption; and the earth tube used thermal con-duction exchange to stabilize indoor temperatures [14]. Differentfrom themany studies that discuss the saving of energy in buildingsby reducing the energy requirements for air conditioning [15,16]through the adjustment of the thermal environment in buildings[17e22] and the use of earth tubes [23e25]. Furthermore, there arevarious evaluation methods are available for using the energy-saving equipments or renewable energy in the buildings. It alsopossible performs on-site simulations and measurements of theenergy-saving use by the various buildings [8,9,26e28]. This paperfocuses on applying energy-saving technology in “MEGA House”open-building project. Using a smart control system to coordinatethe smart control mechanisms and energy-saving equipment helpsobtain the necessary measurement parameters and the best testingsettings in order to evaluate the effects in terms of carbon reductionand economic benefits.

2. Design of experiments

The proposed design for experiments in this paper takes theopen-building “MEGA House” as the case study and considers thedaily habits of the inhabitants and the probable delayed thermaleffects to produce situation simulations. The design of experimentsconducted actual measurements over four stages separated indifferent living day during the course of one year (the durationscover summer (Jul.eSep.) and winter (Jan.eMar.)). Besides, theexperiments of each stagewould be conducted separately in similarenvironmental conditions (temperature and humidity). Thus, inorder to obtain the reasonable samples in each measurement,the 3similar climatic days per month from all measured data would beselected by sampling analysis during the summer (or winter).Therefore, the total measured periods are 9 days as small samplesin each simulation and measurement during the summer (orwinter).

2.1. Studied buildings

This paper concentrates on the creative and intelligent open-

building (OB) “MEGA House” project that was completed inNovember 2009. The OB MEGA House (hereafter, MEGA House) is athree-storey building designed to meet specific eco-awareness andenergy saving objectives. The total floor area of this building is357.02 square meters (see section drawing in Fig.1).

The term MEGA is an acronym for the integration of sustainableMaterials, Electronic management, Green building design, andconstruction Automation. This project constructs a creative andintelligent open-building MEGA House that addresses the majorobjectives of energy efficiency and carbon reduction over theconstruction life cycle through the use of information technologyand green design. MEGA House (shown in Fig. 2) integrates inno-vative technologies that include: (a) nano-coatings, (b) sensornetwork system, (c) RFID doorplates (d) an RFID door control sys-tem, (e) insulation glass, (f) earth tube, (g) solar chimney, (h) 3-in-1solar panels, and (i) RFID-LIMS (Laboratory Information Manage-ment System), among other technologies. The following subsectionclarifies the purpose of the energy-saving equipment used in MEGAHouse. Each technology is illustrated in themodel below alongwithits associated aspect (E, G).

2.2. Description of energy-saving equipment

2.2.1. Electronics (“E”)Electronics refers to electronic facility networks. The electronic

equipment required for the present experiment includes: RFID-controlled air-conditioning sensors, smart control system, andsmart meters. This experiment employed RFID-controlled air-con-ditioning sensors to detect the temperature, humidity, and thermalradiation associatedwithMEGAHouse. Besides, thewireless sensornetwork (see Fig. 3(a)) was integrated with the smart control sys-tem to open/close windows automatically and to adjust venetianblinds, air-conditioning, and lights based on the current environ-mental conditions inside MEGA House in order to minimize energyconsumption. Smart meters were used to monitor the electricityconsumption information of MEGA House.

A. RFID-controlled air-conditioning sensors

The experiment employed several RFID-controlled air-condi-tioning sensors in MEGA House to detect temperature, humidity,and thermal radiation. This sensor array was linked into a wirelesssensor network environment, which consisted of spatially distrib-uted autonomous devices that used sensors to cooperativelymonitor physical and environmental conditions at different loca-tions at the MEGA House site.

In addition to one more sensors, each node in the sensornetwork was equipped with a radio transceiver or other wirelesscommunication device, a small microcontroller, and a battery.Therefore, the results of several nodes were aggregated through thesensor network to capture and record the environmental infor-mation of MEGA House. Tmote Sky manufactured by Moteiv wasthe brand of RFID-controlled air-conditioning sensors used in thisexperiment (see Fig. 3(b)). The range of detection for the temper-ature sensors was�40 to 123.8 �C and the range of detection for thehumidity sensors was 0e100% RH.

B. Smart control system

The smart control system is an interactive LCD touch screendevice that provides integrated access in MEGA House to all light-ing controls, air-conditioning controls, window shades controls,ventilator controls, and earth tube compressor controls. The systemresponds to four different inputs: temperature sensors, humiditysensors, CO2 intensity sensors, and thermal radiation sensors,

Fig. 1. MEGA House section drawing.

Fig. 2. Creative and intelligent open-building MEGA House.

Fig. 3. RFID sensor network system.

M.-Y. Cheng et al. / Building and Environment 100 (2016) 215e226 217

whether installed in indoors or outdoors. After receiving the inputs,the smart control system then controls the related energy-savingequipment automatically based on the environmental controllogic (smart control mechanism [13] (see Fig. 4)) in order tomaintain the optimal level of comfort within MEGA House. Thesystem monitors these inputs constantly and responds to thechanging demands of the environment by adjusting/shutting down

equipment as appropriate.

C. Smart meters

Smart meters were installed into the MEGA House to monitorthe electricity information related to the earth tube compressor,air-conditioning system, and LEDs. This information, including the

Fig. 4. The smart control mechanism [7].

M.-Y. Cheng et al. / Building and Environment 100 (2016) 215e226218

real-time and historic data and daily and monthly power demand,was communicated via ZigBee and used as the basis for the eco-nomic analysis conducted in this experiment. Additionally, MEGAHouse users may easily access the website to simultaneouslymonitor all of the smart meters and manage the powerconsumption.

2.2.2. Green building (“G”)Green building refers to “green” building design concepts. In

this experiment, the basic set of green building equipment in-cludes: a solar chimney (paired with exhaust fans) and an earthtube. A solar chimney and earth tube were incorporated into theMEGA House (shown in Fig. 5). The solar chimney circulates freshair using minimal power and the earth tube uses thermal con-duction exchange to stabilize indoor temperatures. This experi-ment conforms to energy conservation design requirements asfollows: (a) collect simulation parameters; (b) validate and imple-ment network system based onmonitoring and response feedback;

Fig. 5. Air circulation mechanism.

and (c) adjust the MEGA House facility to strike an optimal balancebetween comfort and energy use.

A. Earth tube

An earth tube is a heat exchanger arrangement in which a pipeor tube is buried to facilitate the transfer of geothermal energy withair [29]. In MEGA House, a 40 cm diameter earth tube system wasinstalled beneath the ground to a depth of 4.2 m. The system travelsbeneath the ground outside of Mega House for about 50 m beforepassing through two shafts (shown in Fig. 6). This earth tube ismainly comprised of a PVC pipingmaterial that impregnated with anano-coating on the interior surface. Awindmill that is installed onthe intake end facilitates air convection. This system is designed toutilize the near-constant ground temperature to either extract orreject heat energy to or from the incoming air stream with theground. Outside ambient air passing through the earth tubes iseither heated or cooled before entering MEGA House. In the sum-mer, the earth is cooler than the outside air temperature and the airis thus cooled as it passes through the tubes; the opposite occurs inthe winter.

B. Solar chimney (exhaust fans)

Pollution and the desire to use alternative energy sources haveled to a new environmental approach to MEGA House design. Asimple description of a solar chimney is a vertical shaft that utilizessolar energy to enhance natural stack ventilation through a build-ing. A solar chimney directs warm air inside the chimney causing itto rise out the top and drawing air in from the bottom through aearth tube to ventilate the MEGA House (see Fig. 5). Naturalventilation can be created by providing vents in the upper level ofMEGA House to allow warm air to rise by convection and escape to

Fig. 6. MEGA House earth tube.

M.-Y. Cheng et al. / Building and Environment 100 (2016) 215e226 219

the outside. At the same time cooler air can be drawn in throughvents located in the lower level.

A solar chimney with exhaust fans enhances the natural venti-lation process. The chimney structure must extend higher than theroof level and be constructed on the wall facing the direction of thesun. Furthermore, the openings of vents in the chimney should faceaway from the direction of the prevailing wind. The added advan-tage of this design in MEGA House is that the system may improveventilation rates in the summer and provide a reverse effect duringthe winter to provide solar heating.

2.3. Situation simulations and experimental layout

Based on the above purposes of the energy-saving facilities inMEGA House, the present experiment designs a series of simula-tions and measurements to validate the benefits of energy con-servation. This experimental design is divided into four stages, asdescribed in the following subsections.

2.3.1. The 1st experimental stageIn order to simulate a normal living environment, MEGA House

was naturally ventilated to balance the initial difference betweenindoor and outdoor temperatures prior to starting the energy-saving equipment in the morning.

A solar chimney and earth tube were incorporated into the firstexperimental stage. Natural ventilation was created by providingvents in the upper level of MEGA House to allowwarm air to rise byconvection and escape to the outside. However, in order to enhancethe convection effects, the earth tube fan or solar chimney exhaustfans were operated using mechanical energy to reduce the tem-perature and power consumption throughout the day. Measure-ments in this experimental stage were conducted over a 23-h period started from 8:00 AM to the following morning 7:00 AMand the temperature were recorded every 20 min. Next, these re-sults are compared with the results that used different equipmentsets to gain the best efficiency combination as an openingcondition.

C Testing combinations:

and solar chimney exhaust fans.b. Earth tube (fan) þ Solar chimney: Starting the earth tube

fan and the solar chimney exhaust fans are closed.c. Earth tube þ Solar chimney (exhaust fans): Closing the

earth tube fan and the solar chimney exhaust fans areoperated.

d. Earth tube (fan) þ Solar chimney (exhaust fans): Bothearth tube fan and solar chimney exhaust fans areoperated.

C The required sensor numbers:

The sensor layouts in the experimental design are shown inFig. 7. The required sensors in the first stage are as follows - livingroom: no.13 and no.16, dining room: no.21, master bedroom: no.52and no.53, bedroom (202): no.62, air vent of earth tube: no.31.

2.3.2. The 2nd experimental stageBased on the best efficiency combination in the first experi-

mental stage, the second stage notifies the smart control system toinitiate the best combination and lower the indoor temperaturefirst via a text message or app before the MEGA House user returnshome. The purpose of this experimental stage is to understandclearly the best time to engage the energy-saving combination timeprior to returning to MEGA House in order to lower the tempera-ture and conserve power prior to starting air-conditioners. Therequired sensors in the second stage are the same as those in thefirst experimental stage (see Fig. 7). The following section describesthe process for this experimental stage:

Step 1: Time assumption for returning home

This experiment assumes a normal work schedule and so setsthe time of arrival at MEGA Home as 6:00 PM. Therefore, there is noone in MEGA House prior to 6:00 PM and no energy-savingequipment is thus running earlier than this time. In other words,the house is in a natural ventilation condition with a solar chimneyand earth tube.

Step 2: Set up the measuring time

In accordance with the above conditions, this experiment pro-poses to lower indoor temperature first before the resident returnshome. For this reason, the experiment sets several moments (themeasured time interval is 1 h) prior to the return-home time of6:00 PM in order to assess the relative benefits of energy conser-vation. These are: 1 h prior, 2 h prior, 3 h prior, and 4 h prior.

Step 3: Record temperature and power consumption data ateach testing time.

This experiment lasts for a 4-day period. The best efficiencycombination in the first experimental stage operates at 5:00 PM,4:00 PM, 3:00 PM, and 2:00 PM respectively on each day, thengains the temperature curves and power consumption in these four

Fig. 7. Sensor layouts.

M.-Y. Cheng et al. / Building and Environment 100 (2016) 215e226220

days.

2.3.3. The 3rd experimental stageThis stage discusses the cooling and heating conditions after the

resident returns home to MEGA HOUSE.

A. Cooling test in summer

Continuing the previous situations, the indoor temperature re-mains uncomfortable at the time the resident returns home. TheMEGA House resident chooses whether to use the earth tubecompressor or the air-conditioner to lower indoor temperature.Hence, the testing approach is divided into two parts: (1) start theearth tube (fan) and earth tube compressor set and (2) start theindoor air-conditioner. This section then discusses which equip-ment combination serving two or three spaces conserves moreenergy and then verifies the relative benefit of choosing to use theearth tube. One measurement in the cooling stage lasts 2 h after6:00 PM (recorded every 20 min) and the experimental locationsinclude the living room, dining room, and master bedroom. Thesensors required in this stage are the same as those used in the firstexperimental stage (see Fig. 7).

C Testing combinations (see Table. 1 and Table. 2):

B. Heating test in winter

C Experimental group (master bedroom) (see Fig. 7(b)): Servedby earth tube and solar chimney.

C Control group (bedroom (202)) (see Fig. 7(b)): Servedwithout earth tube and solar chimney.

Because houses need to be kept warm during winter, the earthtube fan is operated during this season as a heater to providewarmth when a MEGA House resident returns home. However, thesolar chimney exhaust fans are not used during this stage becausethe solar chimney exhaust fans may quickly discharge the warm air

Table. 1The testing combinations for two spaces.

Combination no. Equipment comb

(1) Earth tube fan þ(2) Indoor air-condit

Note: Control the indoor temperature at 26 �C.

and lower temperatures indoors. For this reason, the warming ef-fect of using the earth tube in themaster bedroomwas observed forthe heating test (the master bedroom and bedroom (202) doors areall closed), with one measurement period lasting for a 4-h periodafter 6:00 PM (recorded every 20 min).

C Testing combinations:

inations

earth tuionings

a. No energy-saving equipment was operated during thewinter: To compare the temperature consistency betweenthe master bedroom and bedroom (202).

b. When the outdoor temperature is less than 20 �C: Assessthe warming effects of master bedroom served by earthtube fan.

c. When the outdoor temperature is less than 10 �C: Assessthe warming effects.

C The required sensor numbers (see Fig. 7):

Master bedroom: no. 52 and 53, bedroom (202): no. 62, and airvent of earth tube: no. 31.

2.3.4. The 4th experimental stageThis stage integrates the smart control mechanism (see Fig. 4)

into the MEGA House smart control system and operates energy-saving equipment to adjust indoor environmental conditions,including temperature, humidity, and illumination, automaticallythrough the system. The power consumption may be calculatedbased on full-day measurement data to provide an index to theenergy conservation benefits and to the conditions underwhich thesmart control mechanism is used. Therefore, the measurementtime in the 4th experimental stage lasted 15 h from 8:00 AM to11:00 PM and all data were recorded every 20 min.

C Testing combinations:

smart control mechanismb. Operate the equipment without using the smart control

mechanism: Run the air-conditioner all day.

and serving spaces

be compressor (for living room and dining room)(for living room and dining room)

Table. 2The testing combinations for three spaces.

Combination no. Equipment combinations and serving spaces

(3) Earth tube fan þ earth tube compressor (for living room, dining room, and master bedroom)(4) Earth tube fan þ earth tube compressor (for living room and dining room) þ an indoor air-conditioning (for master bedroom)(5) Indoor air-conditionings (for living room, dining room, and master bedroom)

Note: Control the indoor temperature at 26 �C.

M.-Y. Cheng et al. / Building and Environment 100 (2016) 215e226 221

C The needed sensor numbers (see Fig. 7):

The sensors required during the 4th stage are as follows: livingroom: no. 13, dining room: no. 21, master bedroom: no. 52,bedroom (202): no. 62, air vent of earth tube: no. 31.

3. Field measurements and analyses

In order to evaluate the energy and economic performance ofMEGAHouse presented in Subsection 2.3, situation simulations andenergy conservation measurement were carried out on the basis ofthe experimental designs. The design aims to elicit the behaviorrelated to using energy-saving equipment and to identify theoptimal usage combination. A testing analysis was thus carried outin this chapter based on field measurements to investigate thebenefits of the energy-saving equipment.

3.1. Measured energy consumption at the 1st stage

Table. 3 will show the main temperature difference betweenmaster bedroom and bedroom (202) for the earth tube and solarchimney under investigation. The majority of the cold air suppliedto the master bedroom came from earth tube and solar chimney,which demonstrated better temperature-control performance thanbedroom 202.

The average temperature difference between the masterbedroom and bedroom (202) under combination (a) is 0.17 �C (seeTable. 3). The master bedroom gained a lower air temperaturefrom the earth tube and the solar chimney, whereas bedroom 202had a higher temperature because these two pieces of equipmentwere not available. Combination (a), which used neither me-chanical forces nor electricity, achieved a limited temperature-reduction effect. Combination (b), the earth tube fan and solarchimney, was used in the master bedroom and achieved an overallaverage temperature of 29.44 �C, which was below the tempera-ture of bedroom (202). The difference between the two situationsreached as high as 0.54 �C (see Table. 3). This result supports thatusing a mechanically driven earth tube fan enhances the

Table. 3The relative utilization efficiency of energy-saving combinations.

Testing combinations Average temperature (average 9 samples)

Experimental group Control group

Master bedroom (inservice)

Bedroom 202 (noservice)

a. Earth tube þ Solar chimney 30.15 30.32b. Earth tube (fan) þ Solar chimney 29.44 29.98c. Earth tube þ Solar chimney (exhaust

fans)31.43 31.89

d. Earth tube (fan) þ Solar chimney(exhaust fans)

29.12 30.21

Note: 1. Select the 3 similar climatic days per month during summer (Jul.eSep.) (9 samp2. Efficiency ratio (�C/kWh) ¼ Avg. temperature difference (�C)/Avg. power consumption

temperature-reduction effect. By the same token, thetemperature-reduction effects in the master bedroom were goodfor combination (c) and combination (d) (see Table. 3). However,the margin of temperature reduction reached as high as 1.09 �C incombination (d) due to the concurrent use of the earth tube fanand solar chimney exhaust fans to enhance the convection andventilation effects.

Furthermore, in order to select the optimal combination in theexperimental stage, this study calculated the efficiency ratio undereach combination according to the average temperature differencesand the average power consumptions, as shown in Table. 3. Theresults show that combination (d) delivered the best performance(efficiency ratio ¼ 3.39) in lowering ambient indoor temperature.Therefore, combination (d) is used in the analysis conducted in thefollowing experimental stage. Based on the smart control mecha-nism shown in Fig. 4, the operating conditions of combination (d)were defined as:

C When the indoor temperature >15 �C: the solar chimneyexhaust fans are turned on;

C When the indoor temperature <15 �C and the indoor tem-perature >26.5 �C: the earth tube fan is turned on.

3.2. Measured energy consumption at the 2nd stage

The second experimental stage was just carried out in accor-dance with the combination conditions of the earth tube fan andsolar chimney exhaust fans as described in the 1st stage. Thistesting was set up over four time intervals, with data on temper-ature reduction and power consumption recorded each hour andthen converted into an efficiency ratio (shown in Table. 4). Theresults indicate that the temperature reduction is more obviousduring the first hour of each testing time and reaches the higherefficiency ratio of 4.72 �C/kWh at 5:00 PM. Therefore, we obtained apreliminary conclusion at the second experimental stage: MEGAHouse residents may engage the earth tube fan and solar chimneyexhaust fan together 1 h prior to returning home (at 5:00 PM) to

(�C) Power consumption (Avg.)(kWh)

Efficiency ratio (�C/kWh)

Difference (master bedroom-based)

�0.17 0 e

�0.54 0.184 2.93�0.46 0.138 3.33

¡1.09 0.322 3.39

les).(kWh).

Table. 4Results for temperature reduction at each time interval.

Testing time Temperature reduction (�C) Total temperature reduction Total power consumption Efficiency ratio

(18:00-based) 14:00e15:00 15:00e16:00 16:00e17:00 17:00e18:00 (�C) (kWh) (�C/kWh)

1 h ago e e e 1.51 1.51 0.322 4.722 h ago e e 1.27 0.10 1.37 0.64 2.143 h ago e 0.61 0.30 0.12 1.03 0.97 1.064 h ago 0.81 0.25 0.23 0.37 1.66 1.29 1.29

Note: This test averaged the results of four days under similar environmental conditions.

Table. 5Power requirements of different systems to achieve a 1.51 �C reduction in temperature 1 h prior to getting back home.

A Drop of 1.51�C Earth tube (fan) þ solar chimney exhaust (fans) Three air-conditioners

Working time 1 h 20 minPower consumption (kWh) 0.322 (1) 1.24 (2)Power consumption savings (kWh) 0.918 ((2)e(1))

Table. 6The efficiency ratio in cooling test.

Spaceamounts

Equipment combinations Temperaturereduction (�C)

Avg. Powerconsumption (kWh)

Efficiency ratio(�C/kWh)

Twospaces

Earth tube fan þ earth tube compressor (for living room and dining room) 1.13 0.376 3.01Indoor air-conditionings (for living room and dining room) 1.86 1.16 1.60

Threespaces

Earth tube fan þ earth tube compressor (for living room, dining room, and master bedroom) 1.02 0.376 2.71Earth tube fan þ earth tube compressor (for living room and dining room) þ an indoor air-conditioner (for master bedroom)

1.37 0.956 1.43

Indoor air-conditioners (for living room, dining room, and master bedroom) 1.86 1.74 1.07

M.-Y. Cheng et al. / Building and Environment 100 (2016) 215e226222

obtain optimal energy efficiency.Table. 5 estimates the required working time and power con-

sumption of the three air-conditioners to achieve the drop intemperature by 1.51 �C achieved by the earth tube fan and solarchimney exhaust fans. The result indicates that using the earth tubefan and solar chimney exhaust fan combination 1 h prior to gettingback home uses 0.918 kWh less power than using the three air-conditioners in order to lower the temperature by 1.51 �C. Thispower savings (0.918 kWh) is used in the next section as an esti-mated value.

Fig. 8. Average temperature curves under natural ventilation conditions.

3.3. Measured energy consumption at the 3rd stage

3.3.1. Results of cooling test (in summer)This study was conducted under an assumption of a standard

indoor temperature of 28e29 �C. Therefore, average power con-sumption values (shown in Table. 6) were measured under thefollowing environmental setting modes: (a) the outdoor temper-ature is between 28 and 29 �C, (b) the initial indoor temperature is28 �C (if the indoor temperature is higher than 28 �C, it will bereduced to 28 �C first using indoor air-conditioners), and (c) thetemperature settings of indoor air-conditioners and earth tubecompressor are all 26 �C. For the above reasons, the results showthat although the temperature reductions are smaller through theuse of the earth tube fan and earth tube compressor combination,the power consumption is relatively lower, which provides thisapproach with the higher efficiency ratio (3.01 �C/kWh) in thetwo-spaces case. The three-spaces case shows a similar result infavor of the earth tube fan and earth tube compressorcombination.

Table. 6 presents the differences in power consumption betweenoperating the earth tube fan and earth tube compressor combina-tion and operating the indoor air-conditioner. In the two-spacescase, the difference in power consumption is 0.784 kWh. In the

three-spaces case, the difference is as much as 1.364 kWh. Theseresults are applied in the next chapter as inputs in the economicanalysis.

3.3.2. Results of heating test (in winter)This test was conducted to compare the conserved electric

quantity of using earth tube fan with heater in accordance with thesmart control mechanism (see Fig. 4) in winter. Considering resi-dents feel colder indoors in temperatures below 20 �C, this testevaluated the potential use of the earth tube fan as a heater andcarried out related analysis of power consumption and efficiency.

A. All energy-saving equipment switched off (natural ventilation:earth tube þ solar chimney)

Fig. 8 shows the influence of natural ventilation onMEGA Houseduring winter. The temperature trendmeasurements were taken in

Fig. 10. The utility of using earth tube fan in cold current.

M.-Y. Cheng et al. / Building and Environment 100 (2016) 215e226 223

the master bedroom, bedroom 202, outdoors, and the air vent ofearth tube, with results compared to the each other. One finding isthat when the outdoor average temperature was about 12.5 �C onthe testing day in winter, the earth tube exchanged the warm air(about 21.5 �C) from below ground intoMEGA House, with the solarchimney used to enhance the indoor temperature of the masterbedroom. Another finding is that the average temperature of themaster bedroomwas similar to bedroom 202, whichwas not servedby the earth tube and solar chimney. This finding demonstrates thatthe effect of the temperature rise is limited in the natural ventila-tion condition.

B. Outdoor temperature below 20 �C

The simulation time was set from 6:00 PM to 7:00 AM on thetesting day and both indoor and outdoor temperatures wereobserved. Fig. 9 shows a clear temperature trend. When the out-door temperature dropped from 20 �C to 13 �C, the fresh air drawnin through the earth tube fan maintained the indoor temperatureabove 20 �C and maintained an average temperature in the masterbedroom of 21 �C. On the other hand, the average temperature atbedroom 202, which was not served by the earth tube fan, hadtemperature than the master bedroom that was lower by about2 �C. This result supports the good performance of the earth tube inMEGA House of keeping indoor temperatures warm when theoutdoor temperature dropped below 20 �C. Therefore, in theserelatively cold outdoor conditions, an earth tube (fan) may replacethe need for indoor electric heaters in winter.

C. Outdoor temperature below 10 �C:

This test was conducted on a day when the outdoor tempera-ture dropped below 10 �C. Fig. 10 shows that the average tem-perature difference may be as much as 3e4 �C between the masterbedroom and bedroom 202. Although the temperature at the airvent of earth tube dropped to a low of 16.5 �C, it still averaged7.5 �C higher than the lowest outdoor temperature. This differenceindicates an obvious effect of temperature rise in using the earthtube (fan) at lower outdoor temperatures. The difference in tem-perature between the outdoor air and earth tube air makes theearth tube (fan) a viable alternative to an electric heater in colderweather.

According to the above heating test results, the higher temper-ature effect of using an earth tube (fan) is similar to using an electricheater (temperature set as 20 �C) when the range of outdoortemperatures ranges between 15.5 �C and 20 �C. Furthermore,Table. 7 compares the difference in power consumption between

Fig. 9. The warming effect of using an earth tube fan.

using an earth tube fan and a general electric heater in accordancewith the smart control mechanism (shown in Fig. 4) and conductedusing the smart control system in three spaces. This demonstratesthat the earth tube fan may replace the general electric heater toheat the three indoor spaces in a colder environment during winter.This approach has the potential to save about 2.64 kWh/year inpower consumption. A detailed economic analysis follows in thenext section.

3.4. Measured energy consumption at the 4th stage

The experimental stage assumes MEGA House residents remainin the building for the entire day and turn on each equipmentcombination as directed by the smart control mechanism (seeFig. 4) in order to validate the start times for using energy-savingequipment and to obtain the power consumption values gener-ated when using and when not using the smart control mechanism.The experimental conditions were set as follows:

a. Operating time: 8:00 AM to 11:00 PM;b. Outdoor temperature ranges: 28e35 �C; indoor temperature

maintained at 26 �C;c. When the smart control mechanism was not used, indoor air-

conditioners were in use all day;d. The testing place is the living room (one-space condition) and

no use is made of the earth tube compressor.

As shown in Table. 8, the main starting equipment combinationsin the stated testing environment were combination (e) and com-bination (h), with a total power consumption of 18.877 kWh/day.Thus, about 0.637 kWh/day may be saved in that hot climate incomparison with using indoor air-conditioners all day.

4. Economic analysis

4.1. Analytical methodology

The actual cost of electricity and carbon reduction were esti-mated on the basis of the results that were measured in Section 3while the financial cost of CO2 emissions were calculated basedon emissions trading. Therefore, the cost estimates were initiallycarried out in accordance with their equivalent unit values forelectricity and CO2 emissions in this subsection. For these reasons,the financial cost of CO2 emissions and of electricity is evaluated inthe following subsections. However, the cost of electricity is esti-mated in accordance with the electrovalence provided by TaiwanPower Company.

Table. 7The difference of power consumption between an earth tube fan and an electric heater.

Heater equipment (rise in temperature to 20 �C) Power consumption (kWh)/hr Difference of power consumption (kWh)/hr

Earth tube fan 0.184 2.636General electric heater (NP-15ZL) 2.82

Table. 8Evaluating MEGA House power consumption (energyesaving equipment).

Tested combinations Power consumption Operating time

(kWh/day) (％)

Regulated using the smart control mechanisma. Natural ventilation e e

b. Natural ventilation þ Solar chimney (exhaust fans) e e

c. Earth tube (fan) e e

d. Solar chimney (exhaust fans) e e

e. Earth tube (fan) þ Solar chimney (exhaust fans) 1.445 31.1f. Earth tube (fan) þ Earth tube compressor e e

g. Earth tube (fan) þ Earth tube compressor þ Solar chimney (exhaust fans) e e

h. Air-conditioners 17.432 68.9Total power consumption 18.877Without using the smart control mechanismAir-conditioners 19.514 100

Note: All venetian shades were opened during each combination stage.

M.-Y. Cheng et al. / Building and Environment 100 (2016) 215e226224

4.1.1. Cost of CO2

According to the Emissions Trading Exchange, the EuropeanUnion Greenhouse Gas Emission Trading Scheme (EU ETS) is themost widely referenced emissions trading scheme worldwide.Therefore, the Council for Economic Planning and Development,R.O.C uses the European Union Allowances (EUAs) value of USD 22/TON to calculate Taiwan's trade volumes in the carbon market. As aresult, the value of emissions trading is exchanged based on anequivalent unit value of 0.66 NTD/kg, based on a USD:NTD ex-change rate of 1:30.

The emission coefficient for electrical power of 0.636 kg CO2e/kWh was published by the Bureau of Energy, Ministry of EconomicAffairs, R.O.C. in 2008, which generated the value of 0.42 NTD/kWhfor CO2 used in this paper. The formula used is:

Value of CO2 ¼ ð0:66 NTD=kgÞ,ð0:636 kgÞ ¼ 0:42 NTD=kWh

(1)

4.1.2. The cost of electricityMEGA House is a model residential building designed to

consume an average of 308 kWh per month per family [2].Because peak power consumption occurs during the summer, it isreasonable to assume that power consumption may exceed500 kWh from June to September (summer). The Taiwan PowerCompany charges 4.51 NTD/kWh during Jun.eSep. and 3.55 NTD/kWh during Dec.eMar Table. 9 presents the total cost of electricityduring the summer and winter, as estimated from CO2 emissionsand the actual electricity charges from the Taiwan PowerCompany.

Table. 9The conversion forms for summer and winter.

CO2 emissions

CO2e/kWh (kg) Emissions trading valuation (NTD/kg) Mon

Summer (Jun.eSep.) 0.64 0.66 0.42Winter (Dec.eMar.)

4.2. Results of economic analysis

In this paper, an economic analysis was carried out to evaluatethe amount of energy conserved by using energy-saving equipmentinstead of indoor air-conditioners in MEGA House. The economicefficiency was calculated based on the situation simulationsdescribed in Section 2 and the results reported in Section 3. In thefollowing subsections, the economic efficiency will be assessedbased on two different time periods: prior to returning home(before 6:00PM) and after returning home (6:00PM and later).

4.2.1. Prior to returning homeAccording to the measuring and analytical results in Section 3,

the indoor temperature was reduced by 1.51 �C by turning on theearth tube fan and the solar chimney exhaust fans at 5:00PM, 1 hprior to MEGA House residents returning home (see Table. 4). Theresultant savings in power was about 0.918 kWh (see Table. 5),which is the equivalent to a total savings of 4.93 NTD/kWh incomparison with the situation in which indoor air-conditionersare used to reduce the indoor temperature. Therefore, Table. 10estimates the economic efficiency of starting energy-savingequipment prior to returning home during the summer on a ba-sis of the conversion forms shown in Table. 9. As shown, CO2emissions total 52.55 kg and a total of 407.3 NTD/kWh may besaved prior to residents returning to the MEGA House during thesummer.

4.2.2. After returning home

A. Economic efficiency of the cooling test (in summer):

Electric bill (NTD/kWh) Total cost(NTD/kWh)

etary value of CO2 (NTD/kWh)

(1) 4.51 (2) 4.93 (1) þ (2)3.55 (3) 3.97 (1) þ (3)

Table. 10Result (I) of economic efficiency.

Prior to returning home during the summer Power saved (kWh) CO2 emissions (kg) CO2e value (NTD/kg) Cost of electricity (NTD/kWh) Total cost (NTD/kWh)

Transform value 1.00 0.64 0.42 4.51 4.93One hour ago 0.918 0.59 0.39 4.14 4.53One month 27.54 17.52 11.56 124.21 135.77Summer (Jul.-Sep.) 82.62 52.55 34.68 372.62 407.30

Table. 11Result (II) of economic efficiency.

Cooling test in summer (outdoor temperature:28~29 �C)

Power saved(kWh)

CO2 emissions(kg)

CO2e cost (NTD/kg)

Cost of electricity (NTD/kWh)

Total cost (NTD/kWh)

Transform value 1.00 0.64 0.42 4.51 4.93for two spacesPer hour 0.784 0.50 0.33 3.54 3.86Every day (avg.) 2.76 1.76 1.16 12.45 13.61One month (avg.) 82.84 52.69 34.77 373.62 408.39Summer (Jul., Aug., Sep.) 248.53 158.06 104.32 1120.86 1225.18for three spacesPer hour 1.367 0.86 0.57 6.13 6.70Every day (avg.) 4.79 3.05 2.01 21.60 23.61One month (avg.) 143.71 91.40 60.32 648.12 708.44Summer (Jul., Aug., Sep.) 431.12 274.19 180.97 1944.35 2125.32

Table. 12Result (III) of economic efficiency.

Heating test in winter (outdoor temperature:15.5~20 �C)

Power saved(kWh)

CO2 emissions(kg)

CO2e cost (NTD/kg)

Cost of electricity (NTD/kWh)

Total cost (NTD/kWh)

Transform value 1.00 0.64 0.42 4.51 4.93for three spacesPer hour 2.64 1.68 1.11 9.37 10.48Every day (avg.) 16.81 10.69 7.06 59.67 66.72One month (avg.) 504.24 320.70 211.66 1790.05 2001.71Winter (Jan.-Mar.) 1512.72 962.09 634.98 5370.16 6005.14

M.-Y. Cheng et al. / Building and Environment 100 (2016) 215e226 225

This part discusses the economic efficiency of using an earthtube fan with an earth tube compressor instead of air-conditioners to condition air in two and three spaces (see Table.11). The results show that if MEGA House occupants take theformer approach for two spaces, there will be a decrease of about158.06 kg in CO2 emissions and a total cost of 1225.18 NTD/kWhfor cooling during the summer. When the same approach is usedfor three spaces, the savings is even greater: a decrease of about274.19 kg in CO2 emissions and a total cost of 2125.32 NTD/kWhfor cooling during the summer. From the above results, using thecombination of the earth tube fan and the earth tube compressorto condition the air of three spaces in MEGA House is moreeconomically efficient than using air conditioners to achieve thesame cooling results.

B. Economic efficiency of the heating test (in winter):

Based on the above-mentioned results, this subsection assessesthe economic efficiency of using an earth tube (fan) as an electricheater to condition the air in three spaces of MEGA House duringwinter. As summarized in Table. 12 , atotal of 6005.14 NTD/kWh issaved on heating expenditures during thewinter while 962.09 kg inCO2 emissions are eliminated.

5. Conclusions

The scope of the present paper is limited to the creative andintelligent open building “MEGA House”. We analyzed the power

consumption and CO2 emissions related to the use of the energy-saving facilities that were installed in MEGA House. Because theuse of the air-conditioners used more power than the minimumrequirements for the building during the summer, a four-stageexperiment was set up to simulate, measure, and assess the eco-nomic efficiency and the potential for conserving energy. Thissection summarizes the research procedures used and the resultsobtained, with conclusions as follows:

1. The energy conservation facilities in MEGA House hold thestrong potential to enhance the energy conservation efficiencyof “green” buildings.

2. The energy conservation performance achieved by activating anearth tube fan and solar chimney exhaust fans 1 h prior to res-idents returning home in MEGA House in order to lower theindoor temperature is better than the performance achieved byusing air-conditioners.

3. Activating the combination of earth tube fan and earth tubecompressor in order to reduce the indoor temperature afterreturning home achieves good energy conservation perfor-mance when the temperature outdoors is in the range of27e29 �C. Furthermore, MEGA House residents may operate theearth tube fan instead of an electric heater to raise indoortemperatures.

4. Using the smart control mechanism to operate the earth tubefan and solar chimney exhaust fans lowers the indoor temper-ature in MEGA House about 1e2 �C during the summer. Using

M.-Y. Cheng et al. / Building and Environment 100 (2016) 215e226226

the earth tube fan increases the indoor temperature up to3e4 �C during the winter.

5. In terms of economic efficiency, MEGA House regularly savesabout 8537.76 NTD/year in electricity expenditures and de-creases CO2 emissions by around 1288.83 kg/year (sums given inTables. 8e10).

Acknowledgments

Our sincere thanks to the Project of Architecture and BuildingResearch Institute, Ministry of The Interior “Applied Research andPromotion of RFID in MEGA House” for partially funding (Grant No.99A1007).

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Further reading

[30] Endrik Arumagi, Targo Kalamees, Analysis of energy economic renovation forhistoric wooden apartment buildings in cold climates, Appl. Energy Vol. 115(2014) 540e548.

[31] F. Al-Ajmi, D.L. Loveday, V.I. Hanby, “The Cooling Potential of Earth-air HeatExchangers for Domestic Buildings in a Desert Climate”,, Build. Environ. Vol.41 (No.3) (2006) 235e244.

[32] H.J. Wu, S.W. Wang, D.S. Zhu, Modelling and Evaluation of Cooling Capacity ofEarth-Air-Pipe Systems, Energy Convers. Manag. Vol. 48 (No.5) (2006)1462e1471.

[33] K.H. Lee, R.K. Strand, in: “Implementation of an Earth Tube System intoEnergyplus Program”, Proceedings of SimBuild, MIT, Cambridge, Massachu-setts, 2006.

[34] F. Al-Ajmi, D.L. Loveday, V.I. Hanby, The Cooling Potential of Earth-air HeatExchangers for Domestic Buildings in a Desert Climate, Build. Environ. Vol. 41(No.3) (2006) 235e244.

[35] J. Henkel, B. Chen, M. Liu, G. Wang, in: Analysis, Design and Testing of an EarthContact Cooling Tube for Fresh Air Conditioning”, Proceedings of ASME SolarConference, ISEC2004e65086, Oregon, Portland, 2004.

[36] R. Kumar, S. Ramesh, S.C. Kaushik, Performance evaluation and energy con-servation potential of earth-air-tunnel system coupled with non-air-conditioned building, Build. Environ. Vol. 38 (No.6) (2003) 807e813.

[37] C.P. Jacovides, G. Mihalakakou, An underground pipe system as an energysource for cooling/heating purposes, Renew. Energy Vol. 6 (No.8) (1995)893e900.